It is commonly accepted that the service performance of current composite resin systems used in dentistry, such as anterior and posterior restoratives, need substantial improvement. In order to make needed improvements in composites we must more fully understand what causes deficiencies in existing systems, which calls for improved characterization techniques. In addition, to adequately evaluate new chemical concepts for improved composites it is also very important to have improved characterization techniques. As an example, a better understanding is needed for what happens at the molecular level when composites are exposed to the very aggressive environment of the oral cavity. In consideration of the above, this pilot proposal has a novel two-part thrust. First, the proposal outlines studies for the development of electron spin resonance (ESR) imaging as an extraordinarily powerful method for observing diffusion and changes at the molecular level in composites. The method, heretofore unexplored for dental composites, holds great promise for giving new and significant information on the characteristics of dental materials. Secondly, we propose to demonstrate that ESR imaging is an excellent tool to help guide the synthesis, characterization, and development of new chemistry for improved performance composites used in dentistry and other biomedical applications. In the initial effort, model (control) resin systems and currently available visible light cured (VLC) composites will be aged in water at 37 degrees C for various time segments, with the water containing a soluble nitroxide spin probe. ESR imaging will be used to study non-homogeneous, hygroscopic expansion or swelling characteristics of the VLC materials. Measurement of diffusion rates and/or processes and changes at the molecular level, due to water sorption, will be one area of ESR study, with results compared with gravimetric analysis and NMR imaging data. At the same time, the ESR technique will be examined for study of the failure mechanisms of both commercial and control dental biomaterials. The model system will be formulated to be more hydrophobic than existing composites, have greater creep resistance, improved compressive strength, etc., as compared to BisGMA based (control) VLC systems. Characterization methods developed in this study should help ascertain what materials currently in the market place are most worthy of use and how they may be modified to achieve improved performance. Thus, achieving the intended goals should facilitate bringing to the dental chair improved performance materials, contributing to enhanced dental health.